Session Initiation Protocol (SIP) [1] is adopted as the main signaling protocol for the IP Multimedia Subsystem (IMS). Large deployment of SIP servers in Next Generation Networks (NGN) requires studying the behavior and performance of SIP servers under both normal and overload conditions, which may happen in such networks with a vast number of users. In this paper a measurement-based study is performed to assess SIP proxy server performance under different configurations, and for different underlying transport protocols, for both inter-domain and intra-domain calls. Test results show the effectiveness of configuration and distance on SIP signaling performance. Therefore a great attention must be paid during SIP servers deployment.

Carriers have adopted session initiation protocol (SIP) in their next generation networks. Providing carriergrade service requires high availability in times of component failures, avalanche restart, flash crowds and denial of service attacks, which cause overload on SIP servers. Throughput of SIP servers is largely degraded during overload. We propose an SIP overload control (SIP-OC) solution for local and remote situations, working in hop-by-hop and end-to-end modes. Our local SIP-OC method uses a cross-layer approach with negligible performance impact, while the implicit nature of our remote SIP-OC allows detection of sophisticated overload conditions such as those caused by non-SIP entities. Our remote SIP-OC uses transaction response time as the basis for implicit overload detection. Coupling our local and remote SIP-OC schemes, we show that the range of 'sustainable' overload that can be imposed on the system improves significantly. Moreover, incorporating a 2-means filtering mechanism into our SIP-OC scheme makes it perform well under packet-loss. We also show that our proposed solution is robust to network latency and SIP server capacity fluctuations. All of our results are obtained from experiments over SIP testbeds including an experimental IP multimedia subsystem. Figure 1. Basic session initiation protocol signaling (not showing DNS and location server for simplicity).In this paper, we propose a total SIP overload control (SIP-OC) solution including a remote SIP-OC mechanism operating between two SIP servers, namely, AIWB ‡ and a local SIP-OC scheme with almost no performance impact used at the edge, namely, SYN-dropping § . Unlike other local SIP-OC approaches, SYN-dropping is a cross-layer approach and is only triggered for independent SIP UAs running over TCP, while back-to-back user agents (B2BUA), which are in fact dense port SIP clients use AIWB. For experiments, we adopt TCP at the UA-edge and UDP at the edge-core segment of the SIP network. Nevertheless, UDP SIP clients can still continue to connect to the edge proxy. At the core, UDP is used, which improves scalability [11]; however, AIWB can operate on top of any transport mechanism as it resides entirely in the SIP layer.We will show the benefits that can be gained from combining an implicit remote SIP-OC mechanism with SYN-dropping in terms of improved network sustainability over a large range of overload. We use transaction response time (TRT) denoted by TRT (time from INVITE to any provisional response such as, 183-Session-In-Progress/OK/etc.) measured by the upstream server as an implicit indication of overload at some downstream server. Using this information, the upstream server controls the signaling load imposed on the downstream server using an adaptive window-based approach without any assistance from the overloaded server.Although we do not argue against the use of explicit SIP-OC methods, our point is to show the added benefit and feasibility of using an implicit SIP-OC mechanism, which can be integrated alongside an explicit SI...